This invention relates generally to method and apparatus for processing strand material in a processing line having a plurality of stations where work is sequentially performed and particularly in a processing line wherein movement of the strand is continued at a processing station despite halting movement of the strand at another processing station. The invention particularly relates to method and apparatus for indicating when a portion of the strand processed at a first processing station reaches a preselected location in the processing line downstream of said first processing station.
The features of this invention are particularly adapted for use in conjunction with a steel continuous strip annealing line wherein it is necessary to stop a portion of the line in order to attach the leading end of a new steel coil to the trailing end of a preceding steel coil in the line and wherein it is useful to know when the juncture of the two coils reaches a preselected control location downstream of the work station and of a strip accumulator.
While the features of this invention are particularly adapted for use with a continuous strip processing line, it will be apparent that they may be employed in conjunction with other forms of strand material, for example, but not limited to, wire, band, tape, etc. It will be understood that the term "strand," as used herein, may encompass one or a plurality of lengths of strand material and that the lengths may be of random or preselected sizes.
In a continuous strip steel processing line where coils of steel strip are joined end-to-end, it is desirable to know when the beginning of a new coil strip approaches or enters a processing section, particularly when the new coil strip has physical characteristics different from the preceding coil strip. Such knowledge enables process control changes to be applied as the new coil strip enters the processing section. For example, it may be desirable to change the line speed as a strip of different thickness enters an annealing furnace.
It is known in the art to use a looper or other accumulator means ahead of a processing section, where the strip can not be feasibly stopped, e.g. in an annealing furnace wherein stopping of the strip would be detrimental to the quality of the strip. To facilitate continuous movement of the strip through the annealing furnace it is necessary to join, as by welding, coils of steel in end-to-end fashion. However, in order to carry out the joining process, movement of the trailing edge of a first coil must be halted while a leading edge of a second coil is being joined to the first coil. Thus the entry looper in a continuous strip line permits the strip in the annealing furnace section to continue running while the strip at the joining station is stopped.
It is also known in the art to provide methods of detecting the weld between contiguous strips when the weld reaches a downstream location in the processing line. One of the methods comprises punching a hole adjacent to the weld and detecting the hole at the downstream point by means of a light source and photoelectric cell. A disadvantage of such method, in addition to having to punch the holes, is that the hole punching and detection apparatus require considerable maintenance. Another system which has been employed involves the use of thickness variation detection devices; however, a disadvantage of such systems is that they are prone to give false signals when severe buckles are encountered in the strips.